Weaver RG, James MT, Ravani P, et al. - Given urine albumin-to-creatinine ratio (ACR) and protein-to-creatinine ratio (PCR) are employed to measure urine protein, and ACR use is supported by recent guidelines, but for circumstances in which PCR only is available, it would be helpful to have a method to estimate ACR from PCR as precisely as possible, and therefore, researchers developed equations to estimate ACR from PCR in this study utilizing data from a population-based cohort including 47,714 adults in Alberta, Canada, who underwent simultaneous evaluations of urine ACR and PCR. Findings revealed a nonlinear link between log(ACR) and log(PCR), with the implied albumin-to-protein ratio rising from < 30% in normal to mild proteinuria to approximately 70% in severe proteinuria, and with broader prediction intervals at lower levels. The most significant transformer of the link between ACR and PCR was sex; generally, men exhibiting a higher albumin-to-protein ratio. By employing measured ACR and ACR estimated from PCR, similar estimates of kidney failure risk were obtained. In this study, the equations to estimate the median ACR from a PCR were generated, optionally incorporating specified covariates. The likely usefulness of these equations was suggested in certain retrospective clinical or research applications where only PCR is available.